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Vmd designers guide Designer ? s Guide ?? Video Motion Detection This guide describes some of the aspects which should be considered when designing a system incorporating one or more Digital Video Motion Detection systems VMD Site Design for Video Motion

Designer ? s Guide ?? Video Motion Detection This guide describes some of the aspects which should be considered when designing a system incorporating one or more Digital Video Motion Detection systems VMD Site Design for Video Motion Detection VMD By employing sophisticated detection algorithms advanced VMDs have signi ?cantly reduced the number of nuisance alarms found with older technology VMD systems in outdoor environments By following some simple site design techniques the VMD will provide optimum performance with high probability of target detection and low nuisance alarm rates Section to Section describe some these techniques These guidelines also apply to the design of any high quality Closed Circuit Television CCTV system and are not unique to VMD systems Lens Selection and Camera Distance When deciding on the lens required for a particular camera position it is ?rst necessary to decide The type of movement to be detected e g walking people crawling targets or cars The area to be covered i e the ?eld of view The level of security required A general rule for a high probability of detection under varying environmental conditions is that the target of interest should be at least detection zones high or wide for VMDs that process relationships between detection zones For VMDs that analyze on the pixel level then only detection zone is required Do not be confused by the number of programmable detection zones on the screen for units that have then or more are required units that have require only on zone When describing a camera lens system the horizontal ?eld of view is normally restricted to a maximum value The maximum horizontal ?eld of view determines the minimum likely size of a target and the maximum distance between the camera and the target for a particular lens CCamera Format ? Camera Height meters feet Lens Focal Length mm Maximum Distance between the target camera meters feet Dead-zone beneath the camera meters feet Horizontal Field of View meters feet Lens Focal Length mm Maximum Distance bet ween the target camera meters feet Dead-zone beneath the camera meters feet Horizontal Field of View meters feet Figure - The e ?ect of increasing the lens focal length with a constant horizontal ?eld of view Figure - shows the e ?ect of limiting the horizontal ?eld of view to meters feet on the maximum target distance for two di ?erent lenses For a constant horizontal ?eld of view increasing the lens focal length increases both the maximum distance between the target and the camera and the dead zone beneath the camera A typical VMD camera lens design is normally based on a maximum horizontal ?eld of view of meters feet in good lighting conditions At this distance a standing person is approximately to detection zones in height zones VMD or detection zone height zone VMD CIf a larger ?eld of view is used the average light change within a detection zone is smaller and the video movement detection will be poorer Consequently the